Analysis of missing and additional cell defects in sequential quantum-dot cellular automata

The defect characterization of sequential devices and circuits, implemented by molecular quantum-dot cellular automata (QCA), is analyzed in this paper. A RS-type flip-flop is first introduced; this flip-flop takes into account the timing issues associated with the adiabatic switching of this technology and its requirements. It is then shown that a D-type flip-flop can be constructed with an embedded QCA wire which extends over multiple clocking zones. The logic-level characterization of both flip-flop devices is provided. A single additional and missing cell defect model is assumed for molecular implementation. For sequential circuits, defect characterization is pursued. It is shown that defects affect the functionality of basic QCA devices, resulting mostly in unwanted inversion and majority voter acting as a wire at logic level. In this paper, it is shown that a device-level characterization of the defects and faults can be consistently extended to a circuit-level analysis. (c) 2006 Elsevier B.V. All rights reserved.